Inhibiting the corrosion of aluminum



Patented Oct. 12, 1937 J J UNITED STAES PATENT- OFFICE Homer E. McNutt, Rome, Ga., assignor to Tubize Chatillon Corporation No Drawing. Application July 25, 1935,

Serial No. 33,063

8 Claims. (01. -18-54) This invention is concerned with inhibiting the contact with aluminum carriers have resulted corrosion of aluminum and aluminum alloys durin excessive corrosion of the aluminum with the ing exposure to solutions containing alkali metal formation of aluminum salts which are deleterie sulfides. More particularly, the invention is-conous to the artificial silk. Furthermore, because cerned with the prevention of'corro'sion of alumi of the tendency of such solutions to hydrolize 5 num carriers for artificial silk in desulphur'izing into sulphhydrates and the hydroxides of the processes. The invention also contemplates alkali metals the solutions manifest a relatively facilitating the desulphurization of viscose artihigh alkalinity. Probably because of this alkaficial silkfilaments and the production of im-' linity, desulphurizing of artificial silk with solu- 10 proved filaments of this character. tions of alkali metal sulfides usually causes the 10 In the manufacture of artificial silk by the silk fiaments to swell and to become partly viscose process elemental sulphur and complex mercerized. The swelling and partial mercerizasulphur bodies are formed in the coagulation and tion of the filaments appear to increase their reregeneration steps and are entrapped within and sistance to penetration by the solvent for sulphur.

upon the filaments. If these sulphur compounds In any event, when such swelling occurs the 15 areleft associated with the filaments the final rate of sulphur removal is decreased both in'the artificial silk product is of such poo-r appearance desulphurizing bath and in subsequent washing and quality asto be unsaleable. Consequently, operations. 7 a it has been customary to remove these sulphur In other words, the use of aluminum carriers compounds by treating the filaments with a soluin the heretofore customary art of viscose arti- 20 tion which acts as a solvent for such compounds. ficial silk manufacture necessitated the me In several of the heretofore customary procliminary washing and drying of the artificial esses for desulphurizing artificial silk, the masilk and the removal of the yarn from the carrier terial has been subjected to the action of desulin the form of loose skeins which were then de- 5 phurizing solutions in the form of loose 'skeins. sulphurized out of contact with aluminum. Thus, the freshly spun yarn is sometimes col- Another practice of the heretofore customary lected on a bobbin or in a bucket and then Wound art has been to desulphurize the viscose arti into loose skeins which are treated first to reficial silk on the carriers employing solvents move excess coagulant and then to remove sulwhich do not corrode aluminum to an appreciable phur. Another alternative is similarexcept that degree. Such solvents, however, are usually less 30 the yarn is dried after the coagulant is removed; effective than solutions of alkali metal solvents the dried yarn being then wound into loose skeins and are frequently more expensive. 7 which are desulphurized. The prepar'ationand Asa result of my investigations I have dishandling of the loose skeins in either of these covered that the presence of polysulfide sulphur ways is inconvenient and uneconomical. It is in desulphurizing baths containing alkali metal 35 much more desirable to perform the desulsulfides serves a. twofold purpose, in that it inphurizing operation while the yarn is'retained hibits the corrosion ofaluminum and at the on some type of carrier such as a bobbin. Howsame time inhibits the swelling of the artificial ever, when the yarn is desulphurized on a carrier silk filaments. The presence, of polysulfides in 40 it is necessary to provide a carrier material which such desulphurizing baths, therefore, contributes 40 is not attacked by the desulphurizing solution. the following advantages: 7 ""Aluminum and aluminum alloys, on account l. Corrosion of aluminum carriers may be subof their lightness, strength and the ease with stantially inhibited and almost completely pmwhich they can be fabricated, may be used advented; I v

vantageously as materials for constructing V 2. Loss of reagents duerto combination of the 45 bobbins, buckets and other carriers for artisulfides with aluminum is prevented. A ficial silk. The terms aluminum and me 3. The presence of aluminum salts in the yarn tallic aluminum are hereinafter used to include (which has a deleterious elfect upon the final aluminum and aluminum alloys. 7 product) is prevented; and a v a e e Solutions of alkali metal sulfides, for ex 4. Desulphurization of the yarn is accom- 50 amp-1e sodium sulfide, are efficient solvents for plished more rapidly and with greater thoroughr'emoving sulphur from viscose artificial silk. ness. 'Howeven'tliese sulfide solutions tend tooorrode In order to obtain these fourfold advantages, I aluminum, In the heretofore oustomary art, at have found it desirable to maintain a relatively tempts to use solutions of alkali metal sulfides in high concentration of polysulfide sulphur in the 55 proximately. 1.0 gram .per liter of solution. is.

desulphurizing solution. The molecular ratio between polysulfide sulphur and alkali metal monosulphide in the solution should be at least unity. When very concentrated solutions of alkali metal sulphides are used, I have found it advantageous to have slightly more than one molecule of polysulfide sulphur per molecule of alkali metal monosulphide in the solution.

A specific example of a satisfactory desulphurizing solution prepared in accordance with, my invention may be conducive to a more thorough understanding of my. invention. A solution containing approximately 2.4 grams per liter of sodium monosulphide is prepared by dissolving the commercial salt (NazS) in water. To this solution flowers of sulphur equivalent to apadded. The solution is then thoroughly agitated to accomplish a solution of the elemental sulphur as polysulphide sulphur. The solution is then ready for use.

The molecular ratio of elemental or polysulphide sulphur to sodium monosulphide in the above solution is: a

The elemental sulphur combines with the sodium monosulphide to form a polysulphide having a formula which may be exemplified as:

NazSrSx That is to say, additional sulphur is added to the monosulphide, the atomic proportions of the amount added being equal to the subscript :c.

As previously indicated, a: should be approximately 1. The term polysulphide sulphur as used in this application refers to the sulphur Sx which is added to the monosulphide molecule. The term monosulphide sulphur is used to indicate the normal sulphur content of alkali metal monosulphides, i. e. the S in NazS.

The above described desulphurizing solution may be used either in a hot or in a cold condition, but very satisfactory results are obtained when the temperature of the solution during the desulphurizing treatment is maintained between 20 and 30 C. The solution is sucked or forced through the yarn for a period sufiiciently long to dissolve and extract substantially all of the sulphur from the filaments. The yarn is then given a final wash with water. The yarn may then be treated directly or subjected to other customary subsequent treatments, such as bleach- The application of my invention is not limited to the protection of aluminum carriers alone. My invention also permits the use of other aluminum equipment such as tanks for handling alkali metal sulfide solutions used for desulphurizing.

Although the specific example given describes the addition of flowers of sulphur to the solution in order to produce the required polysulphide content, other sources of sulphur may be used conveniently. I have discovered that it is possible to produce satisfactory solutions by mixing fresh monosodium sulfide either as a solid or in the form of a concentrated solution with Waste solutions withdrawn fromthe desulphuriz ing operation. 'By waste solutions, I means those solutions which have dissolved such large quantities of sulphur from the filaments as to be no longer useful as solvents in their unchanged condition. Of course, when starting with fresh solutions it is desirable to add sulphur in the form of elemental sulphur so that the correct ratio of polysulphide sulphur to sodium or potassium monosulphide will be obtained immediately. In a continuous process, however, I have found that the correct ratio of monosulphide to polysulphide sulphur can be maintained merely by adding fresh sodium monosulphide to the desulphurizing solution from time to time. The amount of solution which is lost by entrainment in the filaments is normally sufficient to bleed excess polysulphide sulphur from the bath. When high concentrations of alkali monosulphides are used (say 20 grams per liter), the entrainment loss of polysulphides may be too great to permit the maintenance of the correct ratio of monosulphide and polysulphide sulphur in the bath. In such case it may be necessary to add polysulphide sulphur (say in the form of fiowers of sulphur) to the bath from time to time. By periodically analyzing the desulphurizing bath it may easily be determined whether or not to add alkali metal monosulphide and/or polysulphide to the bath.

Although my invention has been described with particular reference to the desulphurizing of viscose artificial silkin the presence of aluminum, it will also be clear that my invention is applicable to the desulphurization of viscose artificial silk when no aluminum is present, in that by maintaining the ratio of polysulphide to monosulphide sulphur in said solution at a sufficiently high concentration the swelling of the artificial silk filaments is prevented. Removal of the sulphur from the filaments is thus facilitated and accelerated.

My invention is applicable both to yarn which has been dried and to freshly spun filaments. The process may be applied successfully by immersing the artificial silk filaments in the solution, by forcing solutions through the yarn by vacuum or by pressure, and/or by placing yarn and solution in a suitable centrifuge.

I have found that when solutions containing approximately 2.5 grams per liter of sodium monosulphide and 1 gram per liter of polysulphide sulphur are used in the conventional pressure desulphurizing apparatus hours are necessary for a substantially complete removal of the sulphur from the freshly spun artificial silk. When more concentrated solutions are used, or when the temperature of the solution is increased above 30C., the time of treatment may be reduced substantially.

I claim:

1. A process for inhibiting the corrosion of aluminum in the presence of solutions of alkali metal sulfides which comprises maintaining a ratio of polysulfide sulphur to monosulphide sulphur in said solutions of at least unity.

2. A process for inhibiting the corrosion of aluminum in the presence of solutions containing sodium sulfide which comprises maintaining the ratio of polysulfide sulphur to sodium monosulfide in said solutions at least at unity.

3. A process for inhibiting the corrosion of aluminum' in the presence of a solution of alkali metal sulfide which comprises incorporating an alkali metal polysulfide into the solution.

14. In process for desulphurizing viscose artificial silk in the presence of metallic aluminum with a solution containing sodium sulfide the improvement which comprises increasing the sulphur content of the solution to form sodium polysulfide and maintaining the ratio of polysulfide sulphur to monosulfide sulphur in the solutions at not less than unity in order to inhibit corrosion of the aluminum and at the same time to prevent swelling of the viscose artificial silk.

5. In a process for desulphurizing viscose silk involving a preparation of a solution of an alkali metal sulfide and treatment of the viscose silk with the solution, the improvement which comprises incorporating in the solution an alkali metal polysulfide in predetermined amount prior to utilizing it for the treatment of silk.

6. In a process for desulphurizing viscose silk involving the preparation of a solution of an alkali metal sulfide and treatment of the viscose silk with the solution, the improvement which comprises incorporating in the solution alkali metal sulfide in predetermined amount by adding elemental sulphur to the solution prior to utilizing it for the treatment of silk.

'7. In a process wherein artificial silk is desulphurized with a solution containing an alkaline metal sulphide in the presence of metallic aluminum, the improvement which comprises maintaining the ratio of the atoms of polysulphide sulphur to the atoms of monosulphide sulphur in the solution at a point not less than unity by adding to the solution an alkali metal polysulphide, thereby to prevent the corrosion of the aluminum and the swelling and partial mercerization of the artificial silk.

8. In a process wherein artificial silk is desulphurized with a solution containing an alkaline metal sulphide in the presence of metallic aluminum, the improvement which comprises maintaining the ratio of the atoms of polysulphide sulphur to the atoms of monosulphide sulphur in the solution at a point not less than unity by adding to the solution elemental sulphur, thereby to prevent the corrosion of the aluminum and the swelling and partial mercerization of the artificial silk.

HOMER E. McNU'I'I. 

